Biochar‐integrated reactive filtration of wastewater for P removal and recovery, micropollutant catalytic oxidation, and negative CO2e: Life cycle assessment and techno‐economic analysis

Abstract

AbstractLife cycle assessment (LCA) and techno‐economic analysis (TEA) models are developed for a tertiary wastewater treatment system that employs a biochar‐integrated reactive filtration (RF) approach. This innovative system incorporates the utilization of biochar (BC) either in conjunction with or independently of iron‐ozone catalytic oxidation (CatOx)—resulting in two configurations: Fe‐CatOx‐BC‐RF and BC‐RF. The technology demonstrates 90%–99% total phosphorus removals, adsorption of phosphorus to biochar for recovery, and >90% destructive removal of observed micropollutants. In this work, we conduct an ISO‐compliant LCA of a 49.2 m3/day (9 gpm) field pilot‐scale Fe‐CatOx‐BC‐RF system and a 1130 m3/day (0.3 MGD) water resource recovery facility (WRRF)‐installed RF system, modeled with BC addition at the same rate of 0.45 g/L to quantify their environmental impacts. LCA results indicated that the Fe‐CatOx‐BC‐RF pilot system is a BC dose‐dependent carbon‐negative technology at −1.21 kg CO2e/m3, where biochar addition constitutes a −1.53 kg/m3 CO2e beneficial impact to the process. For the WRRF‐installed RF system, modeled with the same rate of BC addition, the overall process changed from 0.02 kg CO2e/m3 to a carbon negative −1.41 kg CO2e/m3, demonstrating potential as a biochar dose‐dependent negative emissions technology. Using the C100 100‐year carbon accounting approach rather than Cnet reduces these CO2e metrics for the process by about 25%. A stochastic TEA for the cost of water treatment using this combinatorial P removal/recovery, micropollutant destructive removal, and disinfection advanced technology shows that at scale, the mean cost for treating 1130 m3/day (0.3 MGD) WRRF secondary influent water with Fe‐CatOx‐BC‐RF using the C100 metric is US$0.18 ± US$0.01/m3 to achieve overall process carbon neutrality. Using the same BC dose in an estimation of a 3780 m3/day (1 MGD) Fe‐CatOx‐BC‐RF facility, the carbon neutral cost of treatment is reduced further to US$0.08 ± $0.01 with added BC accounting for US$0.03/m3. Overall, the results demonstrate the potential of carbon negativity to become a water treatment performance standard as important and attainable as pollutant and pathogen removal.Practitioner Points Life cycle assessment (LCA) of a pilot scale tertiary biochar water treatment process with or without catalytic ozonation at a WRRF shows a carbon negative global warming potential of −1.21‐kg CO2e/m3 while removing 90%–99% TP and >90% of detected micropollutants. Biochar‐integrated reactive filtration use can aid in long‐term carbon sequestration by reducing the carbon footprint of advanced water treatment in a dose‐dependent manner, allowing an overall carbon‐neutral or carbon‐negative process. A companion paper to this work (Yu et al., 2023) presents the details related to the process operation and mechanism and evaluates the pollutant removal performance of this Fe‐CatOx‐BC‐RF process in engineering laboratory pilot research and field WRRF pilot‐scale water resource recovery trials. Techno‐economic analysis (TEA) of this biochar catalytic oxidation reactive filtration process using Monte Carlo stochastic modeling shows a forecasted carbon‐neutral process cost with low P and micropollutant removal as US$0.11/m3 ± 0.01 for a 3780‐m3/day (1 MGD) scale installation with BC cost at US$0.03/m3 of that total. The results demonstrate the potential of carbon negativity to become a water treatmentperformance standard as important and attainable as pollutant and pathogen removal.